US Patent 7579622 Fabrication of MEMS devices with spin-on glass

A method of making an etched structure in the fabrication of a MEMS device involves depositing a bulk layer, typically of polysilicon, prone to surface roughness. At least one layer of photo-insensitive spin-on planarizing material, such as silicate-based spin-on glass, is formed on the bulk layer to reduce surface roughness. This is patterned with a photoresist layer. A deep etch is then performed through the photoresist layer into the bulk layer. This technique results in much more precise etch structures.